just some help with an encryption algorithm

lockmac

Senior member
Dec 5, 2004
603
0
0
Hi there. Just need some quick help if thats ok. Im giong through some examples for a security subject im studying and have the following question:

Consider a simple symmetric encryption algorithm as follows:
1- Input text T and 64 bit key K
2- Divide T into 64 bit size blocks B1...Bn
3- Get first block B1 and perform bit-wise XOR with K to produce encrypted block E1
4- Repeat
a. Get next block Bi and perform bit-wise XOR with Ei-1 to produce encrypted block Ei
5- Until End of Text

(a) Is it a problem if the first block of input happens to be the same as the key? Explain why?
(b) Modify the algorithm to rectify the above problem.


I just need some help with the solutions. I can see that the problem will be that the output will produce all 0's for A.. but does this propose a problem when decrypting the message? Any problems in the key perhaps being worked out?

Any help appreciated thanks
 

Reel

Diamond Member
Jul 14, 2001
4,484
0
76
Try working it out to find out the problem. It should be apparent if you do it by hand.